13-06-2014, 10:53 AM
ELECTRICAL CIRCUITS LABORATORY
MANUAL
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THEORY:
Kirchoff’s current law:
The algebraic sum of the currents entering in any node is Zero.
The law represents the mathematical statement of the fact change cannot accumulate at a node. A node is
not a circuit element and it certainly cannot store destroy (or) generate charge. Hence the current must sum to
zero. A hydraulic analog sum is zero. For example consider three water pipes joined pn the shape of Y. we
defined free currents as following into each of 3 pipes. If we insists that what is always
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Check your connections before switch on the supply.
3. Vary the regulated supply.
4. Measure the current using ammeter.
5. Note the readings in the tabulation.
6. Compare the observation reading to theoretical value.
Superposition theorem
In a linear circuit containing more than one source, the current that flows at any point or the voltage that
exists between any two points is the algebraic sum of the currents or the voltages that would have been
produced by each source taken separately with all other sources removed.
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Check your connections before switch on the supply.
3. Determine the current through the load resistance.
4. Now one of the sources is shorted and the current flowing through the resistance IL measured by
ammeter.
5. Similarly, the other source is shorted and the current flowing through the resistance IL measured by
ammeter.
6. Compare the value obtained with the sum of I1&I2 should equal to I
7. Compare the observation reading to theoretical value.
8. switch off the supply
9. Disconnect the circuit.
Norton’s theorem:
Any linear active network with output terminals can be replaced by a single current source. Isc in parallel
with a single impedance Zth. Isc is the current through the terminals of the active network when shorted. Zth is
called Thevennin`s impedance.
Current through RL= Isc Zth/( Zth+ZL)
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Check your connections before switch on the supply.
3. Find the Norton’s current (or) short circuit current in load resistance.
4. Replace voltage source by internal resistor.
5. Determine the equivalent’s resistance.
6. Find IL by using Norton’s formula.
7. Compare the observation reading to theoretical value.
8. switch off the supply
9. Disconnect the circuit.
THEORY:
Mesh is defined as a loop which does not contain any other loops within it. It is a basic important
technique to find solutions in a network. If network has large number of voltage sources, it is useful to
use mesh analysis.
Node is defined as a point where two or more elements meet together .But only nodes
with three or more elements are considered. If the circuits consists of `N` nodes including the reference
node, then (N-1) nodal equation is obtained.
To apply Mesh analysis :
Select mesh currents .
Write the mesh equation using KVL.
Solve the equation to find the mesh currents
To apply nodal analysis:
Identify & mark the node assign node voltages.
Write the kirchoffs current law equations in terms of unknowns .Solve them to find the
node voltages.
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PRECAUTION:
· Before giving connection all the power supply should be switched off.
· Before switching on the power supply, ensure that the voltage adjustment knob is in
minimum position and the current adjustment knob is in maximum position
PROCEDURE :
MESH ANALYSIS:
· The given circuit is solved for mesh currents I1 &I2 using mesh analysis.
· Connections are made as per the circuit diagram.
· Mesh currents are measured and compared.
NODAL ANALYSIS:
· The given circuit is solved for nodal voltages V1 & V2 using mesh analysis.
· Connections are made as per the circuit diagram.
· Nodal voltages are measured and compared
Electrical devices are controlled by switches which are closed to connect supply to the device, or
opened in order to disconnect the supply to the device. The switching operation will change the current and
voltage in the device. The purely resistive devices will allow instantaneous change in current and voltage.
An inductive device will not allow sudden change in current and capacitance device will not allow
sudden change in voltage. Hence when switching operation is performed in inductive and capacitive devices,
the current & voltage in device will take a certain time to change from pre switching value to steady state value
after switching. This phenomenon is known as transient. The study of switching condition in the circuit is called
transient analysis.The state of the circuit from instant of switching to attainment of steady state is called
transient state. The time duration from the instant of switching till the steady state is called transient period. The
current & voltage of circuit elements during transient period is called transient response.
FORMULA:
Time constant of RC circuit = RC
PROCEDURE:
· Connections are made as per the circuit diagram.
· Before switching ON the power supply the switch S should be in off position
· Now switch ON the power supply and change the switch to ON position.
THEORY:
When two coils are placed nearby and current passes through any one or both of the coils, they become
magnetically coupled. Then the coils are known as coupled coils. If the coils are part of a circuit, the circuit is
known as a coupled circuit. A Single tuned to resonance.
FREQUENCY RESPONSE OF SINGLE TUNED CIRCUITS:
The variation of the amplification factor or output voltage with frequency is called the frequency
response. It can be observed that the output voltage, current and amplification depend on mutual inductance at
resonance frequency. The maximum amplification depends on M and it occurs at resonance frequency.
Amplification factor is given by,